Drawing instrument



Aug. 29, GRAHAM DRAWING INSTRUMENT Filed Dec. 16. 1931 2 Sheets-Sheet l Inventor Allorney Aug. 29, 1933- J. H. GRAHAM DRAWING INSTRUMENT Filed Dec. 16. 1931 2 Sheets-Sheet 2 L/UHH f7! EPA/1AM Inventor Allorney Patented Aug. 29, 1 933 emit a i s PATEN OFFICE DRAWING INSTRUMENT 1 John Graham, Spokane, 7 Application December 16, f193'1 a Serial No. 581,318" i 1 claim. (or. 33-75) r present inventionv relates to an improved drawing instrument of the pivoted, straight edge,

protractor type, for use preferably in combination with a T-square or similar straight-edge instru- '5 ment, by engineers, draftsmen and others,in.pro-

jecting angular lines; cross-hatching sectional drawings, and for various other purposes.

fhe primary object of the invention is the provision of an instrument of this character which 10 is comparatively simple in construction, and

which may be adjusted to angles within the fullcircle of 360, with facility and accuracy, and

my invention. While the drawings show one acceptable exemplification of the invention, it will be understood that the changes and alterations may be made therein, within the scope of my appended claim, without departing from the principles of the invention.

Figure 1 is a plan view of the instrument with the blade in perpendicular positionv to the base, and in dotted lines showing one angular adjustment of the blade or straight edge. I

Figure 2 is an enlarged, interior view of a portion of the laminated post, disclosingthe spring pressed detent forthe sector Figure 3 is a vertical sectional view through the laminated post, and showing the pivotal arrangement and securing means for the sector.

Figure 4 is a perspective view of the spring pressed detent, detached, and Figure 5 is a per-.

V of the lugs 2, 2, or to the straight edge against as which these lugs are used. r

for the practical application of the principles of The base and its post are fashioned from suitable material, as celluloid, preferably with three laminations or, plies, andtheplies are secured together', by;means of screws S, or other suitable fastening means to form a rigid structure. base and post form a triangular, geometrical figure, andvthe post is fashioned with lateral edges 3 that converge toward the pivot head 4 that is fashioned from the intermediate ply of the post, at the upper end of the post, the two outer plies or laminations of the' post being cut away as shown. i v The head 4 provides a pivotal support for the straight edgeblade 5, which has back-edges 6 complementary to the converging edges 3 of the post, and a tenon'6' of the blade is set between The.

the two flanges 7' of the pivotal head '7, which latter is pivoted on the head '4 by'means of the pivot screw 8. The straight-edge blade'is thus provided with rigid flanges and, the latter form the slotted head 7 that is mounted on the singlethickness head 4 of the post.

A sector 9 is provided with a scale of 180 and at its outer peripheral edge thesector is fashioned with notches 10 coincident with thescale mark The sector is guided in its movement by the post 3, andthe post is fashioned with an interior, arcuate slot 12 to receive the sectoras seen in Figure 2.v In addition to the arcuate slot, the post is pro- 0 vided with a recess 13 opening to the arcuate slot and at one side of the post, and another interior slotli communicates with the arcuate slot, said slot 14 being disposed on a line in the plane of the longitudinal axis of the'post and perpendicular to the line connecting the two lugs 2, 2, of the base, 7 Within the perpendicular. slot is enclosed a. spring pressed detent or latch 15, which is fashioned with a wedge-shaped point 16 for engagement with a selected notch 10 of the sector, and at its rear endthe detent is fashioned with opposite- 1y extending lugs 17 that project up into the countersunk openings C. These countersunk openings, of. oval shape as shown, and located at opposite sides of the post, permit ready access of the thumb or finger-to the lugs 1'7 for withdrawing the detent fromthe'sector against tension of a spring blade 18. As best seen in Figure 4 the detentis fashioned at opposite sides with grooves 19, and the spring blade18 is'fashioned with a complementary bifurcated end 20 to fit about or straddle the grooved part of the detent, and the spring blade isanchored at 21 to the lower wall of the recess 13. The spring is thus anchored at one end, and disposed transversely of the post, so that 7 its bifurcated free end tends to urge the detent' into a notch, and hold the detent therein, after the sector is adjusted. A window or opening W is provided in each side of the post in the walls of the arcuate slot, and visible means are thus provided for sighting the position of the sector.

The instrument may be employed for drawing lines or laying off angles at either side of the piv- 0t, and for this purpose it may be turned over bodily, or, the blade 5 may be used at either side of the pivot. Thus, in Figure 1 the blade 5.is set to draw a line perpendicular to the base, at the' left side of the pivot, and it will be apparent that byturning the blade to the right side of the pivot a perpendicular line'may be drawn at that side of thepivot.-

By dotted lines in Figure 1, the b1ade'5 is shown at a angle to the aliiied faces of the lugs 2,2, and the blade is retained in this position by means of the detent in engagement with the notched edge of the sector. In this position the straightedge-of the blade may be usedfor cross-hatching and the instrument is slid along and guided by its straight edge support, as the blade of a T- square, or the straight edge of the blade may be used for projecting a line at the 60 angle from p the horizontal. The blade oi? course may be turned to various angles at the left side of the pivot, and it may be turned on its pivot to the right side of the post for similar use thus permittinga range of 360 'in the use of the straight edge, 7

and thesector.v

Having thus fully described my invention, what I claim as new and desire to secure by Letters Pat-r ent is: V

The combination with a base having a straight .edge and'ia post perpendicular thereto, said post having a' slot therethrough and a pivot head of reduced thickness on the post, of a straight-edge blade of substantially the samethickness as the 

